The present invention relates in general to an agile beam steering device and a method of fabricating the same, and more particular, to an agile beam steering device made of electro-optic (EO) material.
Electrically tunable blazed phase gratings that utilize liquid crystal materials as the electro-optic filter have been proposed recently. Devices of this sort use a layer of liquid crystal sandwiched between parallel transparent substrates. One of the substrates is patterned with closely spaced electrodes, and the opposite substrate may be coated with an uninterrupted common electrode. Application of a linearly changing voltage over a small range of the electrodes induces a linear phase profile in this region. When the linearly changing voltage is periodically applied to the electrodes across the entire liquid-crystal layer, a periodic phase characteristic of a blazing grating is formed.
A common problem of the liquid-crystal beam-steering device is the low efficiency, which is known to be the result of the inability to sharply change orientation at the blaze resets. Sharp phase resets in orientation are prohibited by field fringing. The blaze resets must occur sharply and crisply, or else the “flyback” problem presents in decreased efficiency. Any optical beam propagating through the “flyback” regions cannot be steered as efficiently as required. Therefore, although the liquid crystal beam-steering device is operative to theoretically modulate an optical beam with a steering angle as big as about ±17°, the flyback problem reduces the steering angle to about ±3° practically.
Recently, cascading elements based on electro-optic crystals such as lithium niobate LiNbO3 and lanthanum modified lead zirconate titanate (PLZT) have been developed. These elements provide relatively fine steering angles only. For example, Thomas, et al., have reported a two-stage, phase-array, PLZT-based cascade, which provides steering angles of about ±0.5° with an efficiency of about 50%. For many electro-optic missions, the requirement on field-of-regard (FOR) is coverage of one “cube face”, or a steering angle of about ±54.7°. There is thus a substantial need to develop a large-FOR, agile beam-steering device based on a material having a higher electro-optic coefficient than PLZT.